Method for electro-nickel plating wolfram carbide



United States Patent METHOD FOR ELECTRO-NICKEL PLATING WOLFRAM CARBIDEHarvey L. Slatin, New York, N.Y., assignor to the United States ofAmerica as represented by the United States Atomic Energy Commission NDrawing. Application May 10, 1951 Serial No. 225,680

2 Claims. (Cl. 204-32) This invention relates to electroplating methodsand more particularly, to methods for treating refractory carbides, suchas Wolfram carbide preparatory to electroplating a metal coatingthereon. Specifically, this invention is directed to a method for theelectrochemical etching of Wolfram carbide articles on which a stronglyadherent metal coating can be deposited suitable for attaching anothermetal body thereto.

In certain nuclear apparatus, such as neutron multi plying devices,experimental piles, reactors and the like, a need has long been felt fora method of rigidly attaching some fissionable materials in closeproximity to certain dense refractory neutron reflector materials, such.as Wolfram carbide or cemented Wolfram carbide materials. Prior methodsfor attaching uranium and other fissionable materials to the refractorymetal carbides involved brazing and have been largely unsuccessful,because (1) the brazing materials utilized have reacted undesirably withthe fissionable materials at the temperature of brazing, and (2) becausethose brazing materials do not adhere to the refractory metal carbides,particularly, Wolfram carbide. While the firstmentioned difiiculty canbe surmounted by the use of pure nickel brazing materials the presenceof which are not detrimental from a nuclear standpoint, the problem ofcoating or plating the Wolfram carbide piece is more complicated. Nosimple efficient procedure was known prior to the time of this inventionfor obtaining a deep, uniform etch on Wolfram carbide compositions towhich there could be placed a firm, adherent coat of a metal suitablefor the subsequent non-reactive attaching of the uranium. It wasbelieved that if a firm adherent metal coating could be placed both onthe Wolfram carbide and on the fission-able material, the materialscould be readily and eflectively welded into an integral unit.

It is therefore a primary object of this invention to provide a methodfor obtaining a deep, uniform etch on articles of Wolfram carbide.

It is another object of this invention to provide an electrochemicalmethod for treating Wolfram carbide articles to accept a thin, adherentcoating of nickel.

It is a further object of this invention to provide a simple, eflicientmethod for etching Wolfram carbide articles whereby said articles may beelectroplated with a firm, adherent nickel coating.

It is a still further object of this invention to provide a method fortreating Wolfram carbide articles by electrochemical methods to placethereon a firm, adherent nickel coating which coating is mutuallyadherent .to uranium.

Further objects and advantages will become apparent to one skilled inthe art from the description and example which follow.

The objects of this invention are achieved by a process which comprisesmaking a Wolfram carbide body anodic in an aqueous solution of sodiumpyrophosphate.

During the course of the experimentation with wolf ram carbide materialswhich preceded applicants dis- Patented May 5, 1959- covery it was notedthat electrochemical acid etching solutions were very unsatisfactory.For all practical purposes these solutions produce no discernible etch,or at best, an extremely light etch, entirely unsuited for the purposeof obtaining a firm, adherent nickel coat ing. Other data indicated thata better etch on the wolfram carbide materials could be. obtained withelectrolytes comprising alkaline media. While sodium hydroxide andpotassium hydroxide solutions up to 25 percent concentration gaveimproved results, no deep etch was obtained suitable for the firm,adherent plating of nickel necessary for the attachment of uraniumthereon. Similarly, phosphate baths, such as tri-sodiumphosphate andorthophosphoric acid baths were tried without success. In every case anunsatisfactory etch was obtained on the Wolfram carbide article to whichelectroplated metals, particularlynickel, would not adhere.

A method for obtaining a deep and satisfactory etch was discovered usingan etching solution of sodium pyrophosphate, which method is illustratedin the following example.

Example I A Wolfram carbide disk 3 inches in diameter and /4 inch thickis degreased in trichloroethylene, dipped in a 1:1 nitric acid solutionfor 30 seconds and dried. The disk is then made anodic in an aqueoussolution containing 200 grams per liter of sodium pyrophosphate (Na P Ousing a lead rod inserted in the solution as the cathode. A current ofabout 20 amperes, corresponding to a current density of about 2.0amperes per square inch, is passed through the solution for 10 minutes.The temperature of the solution is maintained at about 60 C. The currentis turned off and the disk withdrawn from the solution, washed in Waterand air dried. A clean, smooth, uniformly etched surface is found tohave formed on the disk. When the etched article is electroplated in anickel chloride solution by one skilled in the art a uniformly adherentdeposit of nickel from 0.0001 to 0.0005 inch thick may be depositedthereon.

The coating as applied in the above example gives excellent bonding forany welding operation and does not chip, flake, peel or otherwise becomenon-adherent under the conditions of welding and heat treatment.

Other embodiments of the invention are possible. For example, the saltcontent of the electrolyte may vary from to 250 grams per liter, thecurrent density may vary from 1 to 5 amperes per square inch, thetemperature of the solution may vary from room temperature, that is,about 20 C., to as high as 60 C., while the etching time may vary from10 to 30 minutes, depending on the other variables. Also, thepretreatment of the piece, that is, the degreasing and cleansing steps,may be varied to apply to the condition of the material undergoingtreatment. Solvents other than trichloroethylene may be used fordegreasing; and the dilute nitric acid dip may comprise a solutionhaving a composition of from 10 to 40 percent nitric acid.

The step of making the Wolfram carbide body anodic in an aqueoussolution composed of sodium pyrophosphate is a forward step in theimprovement for obtaining an :electroplate directly on the Wolframarticle and is particularly useful in a process for welding or brazinganother metal to the Wolfram carbide article. As stated hereinbefore,electroplating techniques used in the past have been unable to provide asatisfactory method for attaching uranium to said Wolfram carbidebodies. The successful application of a nickel plate to Wolfram carbidearticles through the use of the sodium pyrophosphate etching method, hasmade possible a simple, eflicient process for attaching uranium toWolfram in nuclear reactors. By the method of the present invention thenickel plating is attached so firmly to both the.

uranium and the carbide that the attached strips of uranium metal arethemselves ruptured before. separating from the nickel plate.

While many advantages of the present invention will become obvious tothose skilled in the art, it is to be understood that the invention isnot to be limited except as indicated in the appended claims.

What is claimed is:

1. The method of electro-nickel plating articles comprising wolframcarbide which comprises making the article anodic at a current densityfrom 1 to 5 amperes per square inch in :an aqueous solution containingfrom 100 to 250 grams per liter of sodium pyrophosphate for a time offrom to 30 minutes within a tem- 2O perature range of from 20 to 60 (3.,and then electrolytically depositing a nickel coating on the resultantetched surface from an aqueous nickel salt solution.

2,885,329 W a i 2. The method of electro-nickel plating articlescomprising wolfram carbide which comprises making the article anodic ata current density of about 2 amperes per square inch in an aqueoussolution containing about 200 grams per liter of sodium pyrophosphate ata temperature of from to C. for a time of about 20 minutes and thenelectrolytically depositing a nickel coating on the resultant etchedsurface froman aqueous nickel salt solution.

References Cited in the file of this patent UNITED STATES PATENTS923,864 Levy June 8, 1909 1,658,222 Burns et al. Feb. 7, 1928 2,226,384Norris Dec. 24, 1940 2,385,198 Engle Sept. 18, 1945 1,428,141 BurkhardtSept. 30, 1947 2,437,474 Orozco Mar, 9, 1948 2,456,281 Hyner Dec. 14,1948 OTHER REFERENCES Plating, December 1950, pages 1265-1269.

1. THE METHOD OF ELECTRO-NICKEL PLATING ARTICLES COMPRISING WOLFRAMCARBIDE WHICH COMPRISES MAKING THE ARTICLE ANODIC AT A CURRENT DENSITYFROM 1 TO 5 AMPERES PER SQUARE INCH IN AN AQUEOUS SOLUTION CONTAININGFROM 100 TO 250 GRAMS PER LITER OF SODUIM PYROPHOSPHATE FOR A TIME OFFROM 10 T/ 30 MINUTES WITHIN A TEMPERATURE RANGE OF FROM 20* TO 60* C.,AND THEN ELECTROLYTICALLY DEPOSITING A NICKEL COATING ON THE RESULTANTETCHED SURFACE FROM AN AQUEOUS NICKEL SALT SOLUTION.